1. Field of the Invention
The present invention generally relates to plug and receptacle assemblies designed for heavy duty industrial uses and, more particularly, is concerned with a switchable receptacle assembly having an internal interlock mechanism.
2. Description of the Prior Art
Devices, such as plugs and receptacle assemblies, designed for heavy duty industrial uses have been manufactured and marketed for some time by Killark Electric Manufacturing Company, a subsidiary of Hubbell Incorporated, the assignee of the present invention, and by other companies as well. These devices supply electrical power to both fixed and portable electrical equipment including pumps, generators, welders, vacuums, blowers and similar apparatus. These devices are suitable for indoor or outdoor environments and wet, cold, hosedown and corrosive locations commonly encountered in chemical, petrochemical, refining, pharmaceutical, food processing offshore energy, coal mining and many other industries.
Many of these devices have interlock mechanisms to prevent inadvertent removal of plugs from the receptacle assemblies. The interlock mechanism has typically been mounted on the exterior of the receptacle assembly in order to engage an external recess provided in the plug to prevent its removal. A problem which arises with providing the interlock mechanism on the exterior of the receptacle assembly is that this typically has eliminated the use of external threads on the receptacle assembly for reason that external threads would block any radial engagement of the external recess by the interlock mechanism, especially when other supporting structure is considered. The provision of external threads are desired to enable meeting certain industrial rating standards for weather resistance.
Consequently, a need exists for an innovation which will provide a suitable interlock function without sacrificing the provision of external threads on the receptacle assembly.